1. Field of The Invention
The present invention relates to a method for hydrating a cycloolefin to produce a cyclic alcohol. More particularly, the present invention is concerned with a method for hydrating a cycloolefin, in which the hydration is conducted in a reaction system comprising a continuous aqueous phase including water and a crystalline aluminosilicate catalyst suspended therein and an oil phase including a cycloolefin, while dispersing the oil phase as globules having a specific diameter In the method of the present invention, not only can a cyclic alcohol be produced at high selectivity and in high yield, but the activity of the catalyst can also be stably maintained at a high level for a prolonged period of time, and the produced cyclic alcohol can be readily separated.
2. Discussion of Related Art
Various methods for hydrating a cycloolefin by reacting the same with water to produce a cyclic alcohol have been proposed, which include for example, a method in which indirect or direct hydration of a cycloolefin is carried out using a mineral acid, such as sulfuric acid, as a homogeneous catalyst, and a method in which the hydration is carried out using an aromatic sulfonic acid as a homogeneous catalyst (see Japanese Patent Application Publication Specification No. 43-16125/1968). In Example 2 of this published specification, 200 g of an oil phase comprised of a mixture of cyclohexene and cyclohexane is reacted at 90.degree. C. for 12 hours with 160 g of an aqueous phase comprised of water containing p-toluenesulfonic acid. After completion of the reaction, the aqueous phase is separated from the oil phase, and 200 g of water is added to the aqueous phase and subjected to steam distillation while heating. By the steam distillation, cyclohexanol is distilled off to obtain the same. This procedure has drawbacks in that the separation of cyclohexanol as a reaction product from the aqueous phase is not only time-consuming but also disadvantageously causes a large energy consumption.
As a method for coping with the above-mentioned drawbacks of the method using a homogeneous catalyst, a method has been proposed in which a solid catalyst, such as an ion exchange resin, is used (see Japanese Patent Application Publication Specification No. 38-5619/1963 and Japanese Patent Application Publication Specification No. 44-26656/1969). However, this method also has a drawback in that the activity of the catalyst cannot be maintained for a long time because the ion exchange resin is likely to suffer from pulverization due to a mechanical degradation of the resin and because the heat resistance of the resin is unsatisfactory.
As another solid catalyst, the use of a crystalline aluminosilicate has been proposed, which is believed to be advantageous for commercial production of a cyclic alcohol because this catalyst is insoluble in water and excellent in mechanical strength and heat resistance properties. Japanese Patent Application Laid-Open Specification No. 60-104028/1985 (corresponding to U.S. Pat. No. 4,588,846) discloses examples in which a pulverized crystalline aluminosilicate is used as a solid catalyst In particular, this published specification discloses a method, in which water, an aluminosilicate catalyst and cyclohexene as a feedstock are charged in an autoclave reactor equipped with an agitator, and heated at 50.degree. to 250.degree. C. for 15 minutes to 4 hours, followed by isolation of cyclohexanol as a reaction product from an oil phase. The reaction system used in this method is a three-phase heterogeneous system comprised of an oil phase mainly including cyclohexene, an aqueous phase mainly including water and a solid phase including the aluminosilicate catalyst suspended in the aqueous phase. In the conventional method using such a reaction system, problems have often been encountered. Illustratively stated, the conventional method has problems in that when the mixing of the oil phase with the aqueous phase is insufficient, the activity of the aluminosilicate catalyst in the reaction system cannot be fully exerted and therefore the yield becomes unfavorably low. On the other hand, when the mixing of the oil phase with the aqueous phase is too vigorous, an unfavorably long period of time is required in the separation of the oil phase containing a produced cyclic alcohol from the aqueous phase in a stationary zone provided for the separation after completion of the hydration reaction The period of time required for the separation can be shortened by the installation of a large stationary zone, which is, however, unfavorable from the viewpoint of productivity. Further, depending upon the properties of the aluminosilicate catalyst employed and the impurities contained in the catalyst, water and cyclohexene, the reaction system suffers from emulsification to thereby cause the separation of an oil phase including produced cyclohexanol from the aqueous phase to be difficult and cause the catalyst to be leaked into cyclohexanol as a reaction product. Thus, a stable, continuous reaction is difficult to maintain. For breaking such an emulsion, a countermeasure may be conceived which comprises subjecting a reaction product, being formed, containing the aluminosilicate catalyst to centrifugation during the reaction. However, in this countermeasure, it is likely that the centrifuge used is hindered by the adhesion of catalyst deposits, and that the catalyst is disintegrated to thereby hamper the recovery of the catalyst. Accordingly, the above-mentioned countermeasure is not practicable. Further, once emulsification occurs, even if the emulsion is broken to separate the catalyst, the activity loss of the separated catalyst is disadvantageously large as compared to that of the catalyst recovered through the separation of the catalyst from a reaction product containing the catalyst in a stationary zone. Hence, a cycloolefin hydration method free from the emulsification problem has been desired in the art.
Therefore, the conventional methods for hydrating a cycloolefin to produce a cyclic alcohol have been unsatisfactory not only in that the desired cyclic alcohol cannot be obtained in consistently high yield, but also in that the separation of the oil phase containing a produced cyclic alcohol from the aqueous phase after the hydration reaction cannot be efficiently conducted.